1. Filed of the Invention
The present invention relates to integrated circuit technology and to user-configurable circuits. More particularly, the present invention relates to an architecture employing user-programmable interconnect elements.
2. The Prior Art
Antifuses have been used for a variety of programmable products, including gate arrays, PROMs, and programmable silicon circuit boards. Antifuses are usually programmed by placing a high voltage across the antifuse and forcing a current through the antifuse. Programmed antifuses have the characteristic that the final resistance after programming is inversely proportional to the programming current. Generally, a higher programming current produces an antifuse having a lower final resistance. It is usually desirable to obtain the lowest practicable resistance in a programmed antifuse.
The necessity of applying both high voltage and high current to the antifuse complicates the programming circuitry and devices, limits the number of programmable elements which can be implemented, and adds considerable expense to the final product. In some cases, particularly in products which require low final antifuse resistance, programming devices become overly complicated, costly, and result in lower device yield.
A particular problem arises when the interconnection architecture includes significant numbers of internally-located programmable elements (i.e., programmable elements which are not directly connected to conductors which terminate in input/output pins of the device). Providing for access to the internally-located programmable elements during the programming process is often problematic, especially where large numbers of internally-located programmable elements are encountered. This problem is not limited to programmable interconnect architectures employing antifuse elements.
It is an object of the present invention to provide an interconnection architecture which overcomes some of the limitations of programming circuitry and devices.
It is another object of the present invention to provide an interconnection architecture in which programmable elements, including antifuses, located at internal circuit nodes may be initially programmed without the use of relatively high programming currents.
Another object of the present invention is to provide a method for programming the programmable elements in a user-programmable interconnection architecture which avoids some of the shortcomings of prior art programming processes, such as access to internal programmable elements and provision of high programming current to already-programmed antifuses to achieve minimal final resistance.